1. Field of the Invention
The present invention relates to an orthodontic element and a manufacturing method therefor, and in particular relates to an orthodontic element and a method therefor where the element is furnished with a liner provided inside an archwire slot, in order to improve the slippage and shiftability of archwire engaged in orthodontic brackets made of ceramics.
2. Description of the Related Art
In orthodontic clinical treatment, small implements called brackets are attached to the teeth of the patient. In the past, these brackets were mainly made of metal, but in recent years materials such as plastics and ceramics have been developed in order to improve the aesthetic appearance, and now brackets using ceramics have come into use.
The form of use of these brackets is to attach the brackets to the teeth by adhesion, and in order to impart external force to these brackets intended to straighten the teeth, metal archwire is passed through archwire slots provided in the brackets and the archwire and brackets are suitably tied.
However, ceramic brackets particularly in the case of polycrystalline ceramic brackets have the problem of poor slippage on the metal archwire compared to metal brackets.
That is, many polycrystalline ceramics are made by processing their archwire slots with such as diamond blades so that crystal particles are scarified on the processed surface by such slot processing, making the surfaces rough so that the archwire would not slip.
There exists technology intended to improve the slippage of metal archwire on these types of ceramic brackets, as described for example in U.S. Pat. Nos. 5,358,402 and 5,380,196.
This publication describes that it is possible to turn the friction between the archwire slots and the metal archwire into the friction of metal on metal by furnishing metal liners in the slots provided in the brackets.
Further, U.S. Pat. No. 4,988,293 describes that the strength will be reinforced by providing polycrystalline outer coating layers on brackets comprising monocrystalline alumina, which is very fragile.
In addition to the problems above, ceramic brackets are themselves very hard, so that the metal archwire tends to create friction particularly at mesiodistal ends of the slots. Consequently, there is the problem of archwire slippage being worse at the extreme ends than with metal brackets.
This is equivalent to saying that the bracket is hard to slide on the archwire, with the result that tooth alignment does not proceed, and this leads to the problem of longer periods orthodontic treatment.
In the state of affairs, the structure of the ceramics bracket disclosed in U.S. Pat. Nos. 5,358,402 and 5,380,196, because it uses a metal liner, was a step back aesthetically even though slippage improved. Further, with a structure combining ceramics and metal, joining the ceramics and metal is technologically difficult, and brackets having metal liners had the problem of high cost.